1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device. More particularly, the present invention relates to a liquid crystal display (LCD) device and a method for manufacturing the same, wherein spacers in the form of balls are formed in planarized regions to prevent occurrence of steps between the spacers and avoid spacer breakage caused by substrate sagging or vibration.
2. Discussion of the Related Art
With the progress of information-dependent society, the demand for various display devices has increased. To meet such a demand, efforts have recently been made to research flat panel display devices such as liquid crystal displays (LCDs), plasma display panels (PDPs), electro-luminescent displays (ELDs) and vacuum fluorescent displays (VFDs). Some types of such flat panel displays are being practically applied to various appliances for display purposes.
Of these, LCDs are currently most widely used as substitutes for cathode ray tubes (CRTs) in association with mobile image display devices because LCDs have advantages of superior picture quality, lightness, slimness, and low power consumption. Various applications of LCDs are being developed in association with not only mobile image display devices such as monitors of notebook computers, but also monitors of TVs to receive and display broadcast signals, and monitors of laptop computers.
Successful application of such LCDs to diverse image display devices depends on whether or not the LCDs can realize desired high picture quality including high resolution, high brightness, large display area, and the like, while maintaining desired characteristics of lightness, slimness and low power consumption.
Such a liquid crystal display device includes spacers arranged in regions where liquid crystals are filled between the upper and lower substrates that face each other in order to maintain the gap between the substrates. Examples of useful spacers include column spacers fixedly formed in the form of columns and ball spacers in the form of balls.
Hereinafter, a related art LCD device using a ball spacer will be described with reference to the annexed drawings.
FIG. 1 is a sectional view illustrating a related art ball spacer. FIGS. 2A and 2B are sectional views illustrating a phenomenon in which a ball moves and a substrate thus sags.
As shown in FIG. 1, in the liquid crystal display device using the ball spacer, the ball spacer 55 is arranged on the outermost surface of the structure which includes a gate line 51, a gate insulating film 52, a passivation film 53 and a first alignment film 54 arranged on a first substrate 50 in this order.
Meanwhile, as shown in FIGS. 2A and 2B, in the liquid crystal display device using the ball spacer, a black matrix layer 61, a color filter layer 62, an overcoat layer 63 and a second alignment film 64 are further formed in this order on a second substrate 60 that faces the first substrate 50 such that the ball spacer 55 is interposed between the first and second substrates.
The ball spacer 55 may be formed on the first alignment film 54 arranged above the first substrate 50, as shown in FIG. 1, or on the second alignment film 64 formed above the second substrate (represented by reference numeral “60” in FIG. 2A) that faces the first substrate 50.
The ball spacer 55 is formed though a dispersion method. In the dispersion process, the ball spacer is not fixed at the position where the ball spacer is formed, due to the spherical shape thereof, and rolls towards pixel regions, which serve to display an image, as well as the black matrix layer 61, thus causing light leakage. As shown in FIG. 2A, the ball spacer 55 moves down to the metal-free region such as the gate line 51, thus causing occurrence of a height difference between the top of the ball spacer 55 which is arranged in the initial position, and the top of the ball spacer 55 which is arranged in the final position. As shown in FIG. 2B, for the ball spacer 55 arranged in a lower level, the second substrate 60 that faces the ball spacer 55 sags, and the cell gap of this abnormal region (final position) is thus different from that of the normal region (initial position). Furthermore, the difference in the cell gap causes light passage differences, thus resulting in display of different images in respective regions, so-called “display defects”.
As mentioned above, in addition to the problem in which ball spacers roll on the substrate surface where the ball spacers are dispersed, the ball spacers suffer from the problem in that, although being formed at desired positions, the ball spacers deviate from the positions due to external force applied during the manufacturing process or an impact applied in use and thus cause light leakage. That is, when the ball spacer 55 deviates from the original position, it comes out of the portion provided inside the black matrix layer 51 in the normal position and rolls toward the side of the portion. In addition, the ball spacer 55 that deviates from the original position involves further problems in that an aperture ratio is decreased due to the ball spacer 55 arranged out of regions provided by the black matrix layer, and scattering occurs on the surface of the ball spacer 55 which has moved into a pixel region. Furthermore, the ball spacer 55 arranged in the pixel region results in distorted orientation of liquid crystal, thus causing light leakage.
In addition, the movement of the ball spacer 55 may cause damage (e.g., tearing or distorted rubbing) to the surface of the second alignment film 64 that comes in contact with the ball spacer 55 in a dot-like area.
LCDs employing the afore-mentioned related art ball spacers suffer from the following problems.
First, the ball spacers are formed through a dispersion method, thus making it difficult to control the position of formation.
Second, in an attempt to control the position of the ball spacers formed in accordance with the dispersion method, column spacers have been suggested. The column spacers have large areas in contact with the substrate that face the column spacers, and thus high frictional forces, as compared to ball spacers. In this case, upon application of frictional force such as touch, upper and lower substrates shift in one direction, and then take a long time to return to original states thereof due to the high frictional force. In the process of returning to the original states, touch defects occur.
Third, although formed in the desired position, the ball spacers come out of the original positions due to impact or vibration in panel manufacture/assembly processes, thus causing reduction of aperture ratio and light leakage defects.
Fourth, when ball spacers move and repeatedly come in contact with the substrate surface (i.e., alignment film) that faces the ball spacers, the alignment film may be torn or the ball spacers may be broken.